Number Formatting for large integer numbers in Javascript

Question

I know there are in-build function in javascript like toLocalString() to achieve number formatting. But this question is purely for learning and logic understanding.

I have a function in javascript that formats given number in Indian Number formatting standards (eg: 1,234 | 12,21,123 | etc)

Code

function formatter(input) {

    var inputStr = input.toString(), l = inputStr.length;
    var c = 1, f = 0;

    console.log(l);

    for (var x=l-1; x>=0; x--) {

        if (x === 0) {
            continue;
        }

        if (c === 3 && f === 0) {
            inputStr = inputStr.substring(0, x) + ',' + inputStr.substring(x);
            f = 1;
            c = 0;
        } else if (c % 2 === 0 && f === 1) {
            inputStr = inputStr.substring(0, x) + ',' + inputStr.substring(x);
            c = 0;
        }

        c++;
    }

    return inputStr;
}

Now this works for most part (as far as I have test, do point out bugs if you spot any). But my question is how do I handle large number in this, i.e. how do I handle values greater than 9007199254740991.

Answer 1

Hope this now fixes the issue:

function formatter(inputStr) {
inputStr+="";
let c = 1, f = 0;
for (let x=inputStr.length-1; x>=0; x--) {
if (x === 0) continue;
if (c === 3 && f === 0) {
inputStr = inputStr.substring(0, x) + ',' + inputStr.substring(x);
f = 1;
c = 0;
} else if (c % 2 === 0 && f === 1) {
inputStr = inputStr.substring(0, x) + ',' + inputStr.substring(x);
c = 0;
}
c++;
}
return inputStr;
}

//========= Tests =======

console.log(formatter(9007199254740991));
console.log(formatter("900719925474093454549341"));
console.log(formatter("123456678890987665443221112345667676766545434243"));